Valve timing control system for internal combustion engine

Abstract

A valve timing control system includes a timing sprocket, a camshaft, a sleeve secured to the camshaft and accomodated within the timing sprocket. A helical piston assembly and a floating piston are movably disposed in an annular space between the timing sprocket and the sleeve. An end plug is disposed at one end of the timing sprocket to close one end of the annular space. First and second chambers are defined between the floating piston and the end plug and between the floating piston and the helical piston assembly, respectively. A valve spool is operatively connected to an actuator and movably disposed in the sleeve. The valve spool moves among first, second and third positions. At the first position, the first and second chambers are drained. At the second position, the first chamber is communicated with a hydraulic fluid pump and the second chamber is drained. At the third position, the first and second chambers are communicated with the hydraulic fluid pump.

What is claimed is: 
     
       1. A valve timing control system comprising: a timing sprocket including a cylindrical body;   a camshaft;   a sleeve secured to said camshaft and disposed in said cylindrical body and cooperating therewith to define an annular space therebetween;   a helical piston assembly movably disposed in said annular space;   a floating piston movably disposed in said annular space;   an end plug closing one end of said annular space;   said floating piston and said end plug cooperating with each other to define therebetween a first chamber in said annular space;   said floating piston and said piston assembly cooperating with each other to define therebetween a second chamber in said annular space;   means for causing said sleeve to vary an angular position thereof relative to said cylindrical body in response to movement of said helical piston assembly;   a hydraulic fluid pump;   a valve spool movably disposed in said sleeve, said valve spool having a first position wherein said first and second chambers are drained, a second position wherein said first chamber is allowed to communicate with said hydraulic fluid pump to be supplied with pressurized hydraulic fluid and said second chamber is drained, and a third position wherein said first and second chambers are allowed to communicate with said hydraulic fluid pump to be supplied with the pressurized hydraulic fluid; and   an actuator operatively connected to said valve spool for movement of said valve spool among said first, second and third positions.   
     
     
       2. A valve timing control system as claimed in claim 1, wherein said actuator is a solenoid operated actuator of a current proportional type in which said valve spool moves in proportion to electrical current supplied to said solenoid operated actuator.